The challenge to any straight-edged blade, whether Wharnie, sheepsfoot, or Kiridashi style- is sharpening. It is very difficult to keep that edge straight when you hand sharpen it. It's not too bad on a short blade, but as the blade length increases it becomes more difficult. I have a sneaking suspicion this is where most blade designs get the upswept tip. I think blades gravitated that way because so many blades will end up curved over time anyway.
I could be totally wrong about that, of course. Just thinking out loud.